The use of laser beams for machining materials is widespread in industrial manufacturing. For monitoring the machining and for quality assurance, a constant power of an electromagnetic radiation is generated by a laser arrangement and is output with constant parameters. A laser arrangement is provided with a plurality of optical elements that guide and shape the beam. At the same time, the power of the beam is also influenced thereby. The quality of the laser arrangement is essentially determined by the beam orientation, the beam profiling, and the beam power. These parameters can be optimized for the machining processes and can be adversely influenced by aging, incipient destruction, and/or contamination of the optical elements. Such influences in turn adversely affect the beam parameters of the electromagnetic radiation or of the laser beam. In order to record or monitor the parameters, there is the possibility of producing a so-called mode shot of a laser beam. The laser beam generated by the laser arrangement is coupled out from the customary beam path and directed onto a plexiglass cube, where material vaporizes upon impingement of the laser beam and the remaining contour enables a statement about the quality of the beam. This technique is time-consuming and requires an interruption of production.
A brochure from the company Prometec entitled “Laserscope UFC60” discloses a device that enables a continuous measurement and monitoring of unfocused laser radiation from lasers with high power that is principally used in laser machining. The device operates according to the measurement principle according to which a wire increases its electrical resistance if its temperature increases on account of absorbed radiation. In order to determine measurement data, a plurality of grids arranged one above another with extremely thin wires arranged next to one another are provided. An apparatus with two grids mounted one above another is proposed for beam monitoring, wherein this device receiving the grids is to be positioned in a beam path in such a way that the laser beam passes through said grids.
It is difficult to use this device in routine operation of a laser arrangement because a housing receives the grids. As a result, no online measurements can be carried out. Furthermore, the wires provided for recording information can be sensitive since they have a diameter in the lower micrometers range and can break very easily. In particular, a cooling of the grids for an exact measurement is possible with some difficulty since the wires break more easily when there is a strong air flow. Without cooling of the grids, however, the recorded values can be beset with errors as a result of continuous heating of the grids. Furthermore, dirt particles can deposit on the grid and additionally corrupt the measurement results. Moreover, the device cannot be used within a laser apparatus, a beam source, or a beam generator. The contamination, aging, and beginning of the destruction of optical elements cannot be recorded either.
FR 2 698 495 A1 reveals a method for measuring a temperature of a lens provided in a laser arrangement. A first thermoelement fitted at the edge of the lens is provided for recording the temperature of the lens. A further temperature element is arranged on a front side of an exit of the lens outside the beam path. A third thermoelement is fitted at a shoulder of the receptacle. These three thermoelements are respectively arranged in a manner offset by 120° relative to one another and forward the recorded temperature to an evaluation unit. As soon as the recorded temperature has exceeded a threshold value, an alarm signal is output.
By virtue of the arrangement of the thermoelements on the lens and the lens receptacle, individual measurements at the respective contact locations of the thermoelements relative to the lens are carried out by the thermoelements. This does not enable a statement about the determination of the degree of contamination or an incipient destruction or aging and the power of the beam or further beam parameters.
U.S. Pat. No. 4,692,623 discloses a device for recording a situation and a position of a laser beam. The device has a grid of conductor tracks on a glass substrate, the conductor tracks being insulated from one another at the crossover points. The conductor tracks can be covered with a reflective coating. A detector and a display device for recording the change in the electrical resistance on account of the absorbed heat are connected to the conductor tracks.
An analogous arrangement is disclosed in CH 690 796 A5. The mirror disclosed in this document differs from the previous device by virtue of the fact that the grid of conductor tracks is formed in two planes isolated by an insulation. A first layer of a multiplicity of conductor tracks arranged parallel to one another is provided on an insulation on the carrier material of the mirror. The layer is covered with an insulation that, in turn, receives a second layer of conductor tracks running parallel to one another. The second layer of conductor tracks is oriented in a manner rotated by 90° relative to the first layer. The second layer of conductor tracks is also covered by an insulation. Contact areas for connection to an evaluation unit are provided in each case at the outer ends of the conductor tracks.
EP 1 310 782 A1 has disclosed an optical element having a coating on a carrier material. Such optical elements are used for guiding and shaping a laser beam. For recording a situation and a position of a laser beam, it is provided that the optical element has a grid structure composed of thin conductive material on or in the coating or the carrier material. Via contact elements acting on the optical element, the recorded measured values can be forwarded into a measuring device or evaluation unit.
What the three abovementioned devices (found in U.S. Pat. No. 4,692,623, CH 690 796 A5, and EP 1 310 782 A1) all have in common is that a temperature change is brought about in the carrier materials on account of the absorbed radiation, which temperature change is in turn transmitted to the conductor tracks in order to record a change in the electrical resistance in the conductor tracks. However, the temperature change is recorded integrally by means of the respective conductor track, or the length thereof between the two end points. As a result, an evaluation with respect to the beam position and beam size is effected approximately. An evaluation of an intensity distribution of the beam, as is made visible by a mode shot, may not be possible.